Humans are used to dealing with finite things. For the mathematically
inept, infinity is the same thing as a really big number (which is why
some people are impressed when they learn the cardinality of N and Z
are both infinity). Try to imagine what an infinite universe even
means. I can think of some of what it might mean, but not well trained
in physics my brain has difficulty considering the physical nature of
something that's truly infinite. On the other hand, I can easily
imagine a finite universe. We travel far enough and we hit the end of
everything. It might be really far and our universe might be such that
I can't travel to the end of it (or that my movement past the old end
of the universe expands the universe). Finite reasoning is much more
human friendly. Of course, human friendliness does not, in my mind,
indicate anything about it's probability of being an accurate model for
reality.